Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$156.96	12.593%	$176.726	$176.73	$176.75	$176.70
Purchase #2	$242.40	11.649%	$270.6372	$270.64	$270.65	$270.60
Purchase #3	$40.50	13.290%	$45.8825	$45.88	$45.90	$45.90
Purchase #4	$57.53	6.213%	$61.1043	$61.10	$61.10	$61.10
Purchase #5	$60.88	11.106%	$67.6413	$67.64	$67.65	$67.60
Purchase #6	$114.50	4.749%	$119.9376	$119.94	$119.95	$119.90
Purchase #7	$58.86	13.853%	$67.0139	$67.01	$67.00	$67.00
7 purchase totals =	$731.63		$808.9428	$808.94	$809.00	$808.80